(1) Field of the invention
This invention relates generally to utility knives, and in particular to hand-held box cutters of the type used in various trades and crafts to cut sheet material and to open cardboard boxes.
(2) Description of the Related Art
Utility knives, commonly known as box cutters, include a handle in which a blade is secured for cutting a variety of materials. Adjustable-blade utility knives in which a replaceable, single-edge blade having a very sharp cutting edge is slideably-retained within a handle assembly have found widespread use in a variety of industries, for a variety of tasks, for example, shipping-and-receiving, drywall construction, wallpapering and tile-laying. Tradesmen use such utility knives to cut paper stock, plastic sheeting, linoleum, carpets, thin wood panels, wall paper, banding straps, tape and sealed plastic sacks containing bulk materials. Stocking clerks use box cutters to open cardboard cartons, for example in grocery stores, supermarkets, convenience stores, restaurants and other retail establishments.
Of special interest are sealed containers and boxes constructed of paperboard, usually corrugated cardboard, in which individually packaged items are shipped. Typically, cardboard containers are taped or glued shut. When a cardboard container is to be opened, a slicing movement is made by pulling the knife rapidly across the top or side of the container to obtain a clean, straight cut. Sharp blades are required for efficient opening of cartons, and a very sharp single-edged razor blade is commonly used for that purpose. This simple task has resulted in many on-the-job personal injuries.
A cardboard carton is generally held steady in front of the operator with one hand and is cut by pulling the knife with the other hand toward the operator across the top or sidewall of the carton. Because such use frequently involves quick hand movements, and the cardboard presents considerable resistance to cutting, hand and wrist muscle fatigue become a serious concern. Moreover, operator flesh wounds are likely when the knife blade travels free at the end of a cut and catches the operator's hand, fingers, arm, waist or leg. Consequently, special attention must be given to box cutter design features that will protect the operator who must work quickly and repetitively.
Boxes containing goods, such as canned goods, bottles, or other boxed grocery items, are often cut along a top edge around the perimeter of the box to remove a top portion of the box, or around an end edge to remove an end portion, exposing the items therein. It is preferable to cut open the box without cutting the contents within the box. It may be difficult, undesirable, and impermissible to sell merchandise that has been cut while opening the shipping box. For these reasons, it is preferable to make an accurate cut along the top edge of the box that avoids cutting the contents therein by cutting above the contents. On the other hand, persons opening boxes and stocking shelves are often under time constraints and economic constraints regarding the time and cost consumed in stocking the shelves. There is also a comfort factor to consider because a grocery stock clerk, for example, may make hundreds of cuts per day. Therefore, a box cutter needs to be easy to use repeatedly over long periods of time, without impairing operator performance or safety because of muscle fatigue.
Another area of concern is blade access and retention. In conventional box cutter knives, a replacement blade is retained by a keeper plate that is confined in a lower groove and an upper groove formed in the handle. The blade is removed from the knife by extending the keeper plate and blade assembly all the way forward out of the knife, which permits the blade to separate from its engagement with the keeper plate. In some cases, especially when the keeper plate is extended completely forward with some force, the blade will simply fall from the handle by its own weight, resulting in a dropped blade. Thus, improved blade retention means needs to be provided for retaining the blade safely within the handle until such time as access is needed for blade replacement, so that the blade may be manually and safely removed by the operator.
An edge guide on a box cutter provides a number of useful advantages. An edge guide allows an operator to quickly and accurately make a cut at a fixed distance from an edge. A guide allows the operator to repeatedly make cuts at a certain angle. A guide allows the operator to make more consistent cuts. An edge guide also allows the operator to make a cut with less effort and less energy exerted. For example, it is usually easier to make a cut with a pulling motion when the user can lean on the guide while pulling, as the guide slides across an edge. Also, the guide allows the operator to make a cut at a precise location with less effort to maintain a stable position of the blade relative to the edge while cutting. Therefore, the use of an edge guide may allow the operator to make the same number of cuts per day more consistently while using less effort and energy, thereby reducing muscle fatigue.
Conventional edge guides provide ways to accurately and quickly cut along an edge of a box at a certain distance from the edge and at a certain angle. However, box cutters are not only used to make edge cuts, but are also often used for other types of cuts, such as cutting a taped edge, where the fixed guard may interfere with or preclude other types of cuts. Also, some edge guards do not provide safety features that will adequately protect a user during repeated rapid cuts. Thus, a need exists for a utility knife configured for reducing repetitive motion injuries caused by hand and wrist muscle fatigue and thumb manipulation to extend the blade, that will enable the operator to repeatedly, accurately and quickly cut open boxes without cutting the contents therein and without compromising the safety of the operator.
Yet another area of concern in box cutter design is blade extension and retraction, which require a high level of manual dexterity, hand coordination and hand strength. Safety and ease of use have been improved by automatic blade retraction. A conventional box-cutter knife with automatic blade retraction has a housing forming a hand grip handle, a blade holder slidable in the housing, and a blade carried in the holder between a front position in which the blade projects forward from the front end of the housing and a retracted position in which the blade is enclosed within the housing. A spring is provided that continuously urges the blade and holder into the rear position. A thumb button is provided which allows the user to push the blade out and hold it extended for cutting action.
When the thumb button is released, the spring automatically urges the blade in retraction back into the housing. Such a knife is considered safe, since the blade will retract automatically except when the thumb button is extended. However, this arrangement is inconvenient as the operator must maintain pressure on the thumb button to use the knife, which causes muscle fatigue after repetitive use, and prevents the thumb from being used to maneuver the knife and establish a firm grip, resulting in a reduction of stability and control during heavy cutting jobs.